Processes for hydroformylating an olefin to prepare a carbonyl derivative containing one carbon atom more than the parent olefin by reacting the olefin with synthesis gas in the presence of a Group VIII metal, e.g. rhodium, in complex combination with an organic ligand, carbon monoxide also being a component of the catalyst complex, are well known in the art (the "oxo" process) and of growing industrial importance. This technology is summarized, for example, in U.S. Pat. No. 3,527,809 to Pruett et al. The olefin reactant is contacted with the catalyst and the synthesis gas (a mixture of carbon monoxide and hydrogen) in the presence of a liquid reaction medium, which may or may not comprise a separate inert liquid solvent species. The synthesis gas comprising the carbon monoxide and hydrogen is typically bubbled through the liquid reaction medium which is contained in a hydroformylation reactor which can be mechanically stirred or which may be agitated solely by the action of reactant gas being bubbled therethrough. The gas, in addition to hydrogen and carbon monoxide, may also contain vapors of the reactant olefin, in a proportion which will depend upon such factors as reaction conversion rate and the volatility of the olefin.
The aldehyde hydroformylation product can be recovered from the liquid hydroformylation reaction medium in various ways, but, especially when the aldehyde is of comparatively low molecular weight, e.g., when it contains from three to about seven carbon atoms and especially when it contains from three to about five carbon atoms, it is conveniently stripped out in vapor form by distillation, evaporation, or, especially, by being stripped out of the hydroformylation reaction zone in the gases which are being bubbled through the liquid contained therein. Hershman et al have described this technology in "I&EC Product Research and Development" 8, pp 372-375 (1969) in a discussion of hydroformylation of propylene in a gas-sparged reactor.
In more recent years various patents and other publications have appeared directed to the use of special reaction solvents and/or special techniques for stripping the aldehyde product out of the liquid reaction medium. For example, U.S. Pat. No. 4,329,511 issued to Hackman et al describes useful solvents as well as the use of a particular high molecular weight, high-boiling inert liquid reaction solvent in proportions of about 40 to about 95% by weight of the liquid reaction solution for purposes of controlling the rate of stripping at a level such that at a given weight concentration (relatively low) of product aldehyde in the mixture, and the mole fraction of aldehyde in the mixture will be relatively high. The specific solvents used are not considered critical as long as they are: (1) miscible with the catalyst system; (2) miscible with the reactants; (3) miscible with the reaction products; (4) low in volatility so as to facilitate striping reaction product and by-products from it and (5) chemically inert in the hydroformylation reaction system. The disclosed solvents include, for example, alkyl-substituted benzene; pyridine and alkyl-substituted pyridines; tertiary amines; high boiling esters such as dialkyldicarboxylates and triorganophosphates as well as esters of polyols such as trimethylolpropane and pentaerythritol; ketones; alcohols such as butanols; nitriles such as acetronitriles; and hydrocarbons such as kerosene, mineral oil, cyclohexane, naphtha, etc. and aromatics such as biphenyl. The use of polyalkylene glycols such as polyethylene glycol and polypropylene glycol having molecular weights greater than about 700 are stated to be particularly desirable because of their availability and their desirable properties for use as a hydroformylation solvent.
A related hydroformylation process is described in U.S. Pat. No. 4,151,209 to Paul et al, which describes techniques for recovering aldehyde products from the reaction products by distillation, stripping, employing the ratio of phosphorus contained in the high-boiling reaction by-products to the phosphorus contained in the ligand (triorganophophine ligand) which is present, as the primary control. Although the claimed improvement of the Paul et al process is different from that of the process of U.S. Pat. No. 4,239,511, similar solvents have been found to be satisfactory for use in the hydroformylation reactions described in both of these patents.
An alternative catalyst solvent is disclosed in U.S. Pat. No. 4,148,830 issued Apr. 10, 1979 to Pruett et al. As disclosed therein higher boiling aldehyde condensation products are employed as the catalyst solvent. In this patent, liquid effluent from the reaction zone containing catalyst, solvent and gases, is processed to strip and recover the aldehyde product. During this procedure some hydrogen, carbon monoxide, unreacted olefin, and other by-product and inert gases dissolved in the reactor effluent are removed by reducing pressure on the effluent stream to flash off such gases. The desired aldehyde product is then recovered from said effluent and the liquid residue fraction of unrecovered aldehydic product, catalyst and high boiling condensation product is recycled to the reactor. Accordingly, this process has sometimes been referred to as a liquid-recycle hydroformylation process (or "liquid recycle process").
U.S. Pat No. 4,247,486, issued Jan 27, 1981 discloses a hydroformylation process which is directed to further modifications of the basic oxo process disclosed in U.S. Pat. Nos. 3,527,809 and 4,148,830. In this process, unreacted feed, the aldehyde reaction product and higher boiling condensation products, inter alia, are allowed to distill out of the reaction medium such as by being stripped from the reaction medium as previously described. The aldehyde product and condensation products are condensed from the gas stream which contains unreacted feed, (i.e., syn gas and olefin). The gas stream is recycled to the reactor. Moreover, a purge stream comprising gaseous by-product such as propane can be taken from the gas recycle stream to remove such propane and to control its concentration within the process. The purge stream also contains, inter alia, aldehyde product, unreacted olefin inert gases, as well as carbon monoxide and hydrogen. The recovery of olefin from such a stream is impractical and the purge stream is typically used as a fuel.
Likewise, to control total reactor pressure in a liquid recycle process as described above due to build up of inerts and the like, a gaseous purge is generally taken from the liquid recycle hydroformylation reactor, where excess hydrogen, carbon monoxide, unreacted olefin, inerts and alkane by-products, such propane, are vented as off-gas. In addition, during the product separation step in a liquid recycle process, some gases, primarily unreacted olefin and alkane by-product, which remain dissolved in the liquid catalyst-containing effluent, are separated along with the desired aldehyde product. A portion of such separated gases are condensed with the desired aldehyde product. The remaining separated gases can be purged from the system.
The amount of olefin and syn gas components lost by purging in such recycle processes can amount to a significant economic disadvantage over the life of a commercial continuous operation due to the efficiency loss of such purged desirables as unreacted olefin and syn gas.
In German Pat. No. 3,102,281, issued Dec. 23, 1982, a cobalt-catalyzed high pressure hydroformylation of propylene was conducted and the waste gas, resulting from the decobalting of the reaction mix, containing propylene, carbon monoxide and hydrogen, was introduced into a low pressure rhodium catalyzed hydroformylation process, simultaneously conducted. In German Laid-Open Patent No. 3,245,883, published Jun. 14, 1984, flue gas from a low pressure rhodium hydroformylation process containing propylene is compressed and introduced into a high pressure cobalt catalyzed reactor for conversion to aldehyde.
In U.S. Pat. No. 4,593,127 there is disclosed a primary liquid recycle or gas recycle rhodium-catalyzed hydroformylation process for producing aldehydes, wherein an olefin, carbon monoxide and hydrogen are reacted in the presence of a solubilized rhodium-phosphorous complex catalyst, free phosphorus ligand and higher boiling aldehyde condensation by-products to produce an aldehyde product, a gaseous effluent comprising unreacted olefin and any of said aldehyde product, hydrogen, carbon monoxide and an alkane by-product is vented from the process, wherein the improvement comprises conducting a decoupled secondary liquid recycle or gas recycle rhodium-catalyzed hydroformylation process conjointly with the primary process, and the vented gaseous effluent together with make-up carbon monoxide and hydrogen is employed as the reactant feed to the secondary process. The decoupled process of this patent requires its own independent catalyst system and independent product recovery system. A key feature of the invention disclosed therein is that unreacted olefin contained in a vent stream from the primary system can be employed as the sole olefin feed to the decoupled secondary hydroformylation process, i.e. make-up quantities of olefin need not be added to the decoupled hydroformylation process.